1. Field of the Invention
The present invention relates to a fluid supply device which is used in a supply system for fuel or the like to a fuel cell.
2. Description of the Related Art
A solid macromolecular membrane type fuel cell comprises a stack (called a fuel cell) which is made up of a plurality of cells laminated together, each comprising a solid macromolecular electrolyte membrane sandwiched between an anode and a cathode. Hydrogen is supplied as fuel to the anode and air is supplied as oxidizer to the cathode, and hydrogen ions which are generated by a catalytic reaction at the anode pass through the solid macromolecular electrolyte membrane and migrate as far as the cathode, where these hydrogen ions are subjected to oxidizing and electrochemical reaction by the cathode; and thereby generation of electricity is performed.
In order to maintain the ionic conductivity of a solid macromolecular electrolyte membrane, extra water is mixed into the hydrogen which is supplied to the fuel cell by a moisturizing device or the like. Due to this, water accumulates in the gas conduits in the electrode of the fuel cell, and, in order for these gas conduits not to become blocked up, a certain amount of the fuel flowing through these gas conduits is exhausted.
It is possible to make effective use of this exhaust fuel by recirculating it (hereinafter this fuel flow is also termed xe2x80x9crecirculated hydrogenxe2x80x9d) and mixing it into the fuel (i.e. the hydrogen) which is freshly being fed into the fuel cell, and thus it is possible to enhance the energy efficiency of a solid macromolecular membrane type fuel cell.
In the past, as a fuel cell of the type described above, there has been a known fuel cell device which recirculates the fuel in this manner by using an ejector, such as for example the fuel cell device disclosed in Japanese Patent Application, First Publication No. Hei 9-213353.
A typical prior art type ejector, as shown in FIG. 19, includes a recirculation chamber 2 which is connected to a base end aperture of a diffuser 1 and a recirculation conduit 3 which is connected to this recirculation chamber 2, with a nozzle 4 which is arranged so as to be coaxial with the diffuser 1 projecting within the recirculation chamber 2 so that its end opposes the base end aperture of the diffuser 1. With this ejector, when hydrogen which is freshly being fed into the fuel cell is injected from the nozzle 4 towards the diffuser 1, a negative pressure is generated in the throat portion 5 of the diffuser 1, and the recirculated hydrogen which has been conducted into the recirculation chamber 2 is sucked into the diffuser 1 by this negative pressure, so that the recirculated hydrogen and the hydrogen which is being injected from the nozzle 4 are mixed together and are then ejected from the outlet of the diffuser 1. FIG. 20 roughly shows the pressure distribution in the various regions of such a prior art ejector.
The sucking-in ratio provided by the ejector will be termed its xe2x80x9cstoichiometryxe2x80x9d. The meaning of the term xe2x80x9cstoichiometryxe2x80x9d is defined, in terms of this example, as being the ratio (Qt/Qa) of the flow Qt of the hydrogen which is ejected from the diffuser (in other words the total flow of hydrogen supply which is provided to the fuel cell) to the flow Qa of the hydrogen which is ejected from the nozzle (in other words the hydrogen consumption flow). Furthermore, if the flow of the recirculated hydrogen which is sucked in from the recirculation chamber to the diffuser is termed Qb, then, since Qt=Qa+Qb, the stoichiometry can be defined as (Qa+Qb)/Qa. When the stoichiometry is defined in this manner, it is possible to say that the greater is the value of the stoichiometry, the greater is the efficiency by which the ejector sucks in recirculated hydrogen.
Now, since with a prior art type ejector the diffuser diameter and the nozzle diameter of a particular ejector are fixed, it is usual to employ choices for the various diameters which are the most suitable for the fluid flow range which is being utilized. In this case, the fluid flow (in terms of this example, the hydrogen consumption flow Qa) is arranged to be a constant value for which the stoichiometry provided by the ejector is maximum.
FIG. 21 shows an example of experimental results which have been obtained with an ejector for fuel supply to a fuel cell for the relationship between stoichiometry value and hydrogen consumption flow Qa (hereinafter termed the xe2x80x9cstoichiometry characteristicxe2x80x9d) with the nozzle diameter as a parameter, and it will be clear from this figure that: on the one hand although the stoichiometry value is elevated when the nozzle diameter becomes small, the hydrogen consumption flow Qa becomes small; while on the other hand, although the hydrogen consumption flow Qa becomes large when the nozzle diameter becomes large, the stoichiometry value becomes small.
In the case of a fuel cell, the stoichiometry value which is required according to the operating state of the fuel cell (hereinafter termed the xe2x80x9crequired stoichiometry valuexe2x80x9d) is determined as shown in FIG. 21 by the thick solid line, and, since in the case of a fuel cell automobile the hydrogen flow from idling to full output power varies by a factor of 10 to 20, therefore it has been difficult to satisfy the required stoichiometry value over the entire region of hydrogen flow with a single ejector.
In order to solve this problem, a two-stage changeover ejector system has been proposed by the present applicant (in Japanese Patent Application 2000-85291), which changes over between an ejector for small flow which includes a small diameter nozzle and a small diameter diffuser and an ejector for large flow which includes a large diameter nozzle and a large diameter diffuser, and which is fitted with a bypass conduit.
Although with this method it is possible to maintain the stoichiometry characteristic to be satisfactory over a comparatively wide range from a small flow to a large flow, it becomes necessary to provide two ejectors and a flow conduit changeover device; and additionally if, in order further to improve the stoichiometry characteristic, the number of ejectors is increased to 3 or 4, it becomes necessary to change over the fluid flow between these multiple ejectors, which leads to increase of the size and weight of the device, which is most disadvantageous.
Furthermore, in Japanese Patent Application, First Publications Hei 8-338398 and Hei 9-236013 there have been proposed variable flow ejectors, although these are not ejectors for fuel supply to fuel cells.
In the variable flow ejector disclosed in Japanese Patent Application, First Publication No. Hei 8-338398, a rod is included which can shift along its axial direction inside the nozzle, and the aperture area of the tip of the nozzle can be varied by shifting this rod along its axial direction. With this variable flow ejector, it is possible to vary the stoichiometry value by changing the aperture area of the tip of the nozzle in this manner, however, since the diffuser diameter is fixed, this restricts the correspondence relationship between the stoichiometry value and the flow. In this case, it is desirable to set the correspondence relationship which is required by the fuel cell (the correspondence relationship shown by the thick solid line in FIG. 21) in more detail, and to enhance progress in optimization of the stoichiometry value. Furthermore there is the problem that, if the aperture area is made small when the flow is small, the flow resistance due to the wall surface is increased, so that it becomes impossible to obtain the desired stoichiometry characteristic.
On the other hand, in the variable flow ejector disclosed in Japanese Patent Application, First Publication No. Hei 9-236013, the nozzle is made to be shiftable with respect to the diffuser along its axial direction, and a plurality of different nozzles which have different diameters are made available so that it is possible to change over between them. With this variable flow ejector, since it is not possible to vary the nozzle diameter without changing over the nozzle, therefore it cannot be applied as an ejector for a fuel cell which is to be utilized in an automobile, for which variation of the stoichiometry value continuously and moreover over a short time period is demanded.
The objective of the present invention is to provide a fluid supply device for a fuel cell which can deliver the desired stoichiometry characteristic over a wide range of flow.
In order to achieve the above described objective, the fluid supply device for a fuel cell according to the present invention comprises: a needle which has an end portion; a taper section which is arranged coaxially with the needle; a nozzle which has an aperture portion at its end, with the needle and the taper section being coaxially inserted into the aperture portion, and which emits a first fluid from the aperture portion when the first fluid is supplied to the interior of the nozzle; a diffuser which is provided coaxially with the needle, the taper section, and the nozzle, which sucks in a second flow of fluid by a negative pressure which is generated by the injection of the first flow of fluid, and which mixes the second fluid flow with the first fluid flow and supplies the mixture; a needle position adjustment device which shifts the needle along its axial direction; and a taper section position adjustment device which shifts the taper section along its axial direction; wherein the first fluid flow passes through a first fluid conduit which is constituted by a gap between the needle and the aperture portion of the nozzle, and, after mixing with the second fluid flow, flows through a second fluid conduit which is constituted by a gap between the taper section and the diffuser.
According to this invention, since it is possible to vary the ratio between the first fluid flow and the second fluid flow continuously, thereby it is possible to ensure the desired stoichiometry value over a wide range of flow, from small flow to large flow, and also to ensure the entire flow desired. Furthermore since, simply by shifting the needle and/or the taper section in the axial direction, it is possible to vary the ratio between the first fluid flow and the second fluid flow continuously, thereby it is possible to achieve simplification of the device and reduction of its size and weight. Yet further, since there is no requirement to change over between nozzles, this structure can be applied to a fuel cell for an automobile in which the required stoichiometry value changes continuously and moreover over a short time period.
The taper section may be formed integrally with the needle so as to extend from the end portion of the needle, and the needle position adjustment device may also serve as the taper section position adjustment device.
The shape of the needle may be determined so that the stoichiometry value for the first fluid conduit and the second fluid conduit matches a stoichiometry value which has been set in advance in correspondence with flow. By the stoichiometry value is meant the ratio of the sum of the flow of the first fluid flow and the flow of the second fluid flow (hereinafter termed the total flow) to the flow of the first fluid flow.
By utilizing this type of structure it is possible to vary the ratio of the flows of the first fluid flow and the second fluid flow continuously to the desired flow ratio, and accordingly it is possible to obtain the desired stoichiometry value by changing the position of the needle.
A fluid supply device for a fuel cell according to another aspect of the present invention comprises: a needle which has a taper section at its end; a first nozzle which has an aperture portion at its end, with the taper section of the needle being coaxially inserted into the aperture portion, and which emits a first fluid from the aperture portion when the first fluid is supplied to the interior of the first nozzle; a diffuser which is provided coaxially with the needle and the first nozzle, and which sucks in a second fluid flow by a negative pressure which is generated by injection of the first fluid flow, mixes the second fluid flow with the first fluid flow, and supplies the mixture; a second nozzle which has an aperture portion which faces the diffuser, and which is capable of emitting the first fluid flow from the aperture portion; and a needle position adjustment device which shifts the needle along its axial direction; wherein the first fluid flow is capable of being supplied to the diffuser from a gap between the needle and the aperture portion of the first nozzle, and the first fluid flow is capable of being supplied to the diffuser from the second nozzle.
According to this device, when a first fluid flow of small flow is supplied to the diffuser, it is possible for this first fluid flow to be supplied to the diffuser only from the second nozzle, while, when a first fluid flow of large flow is supplied to the diffuser, it is possible for this first fluid flow to be supplied to the diffuser both from the gap between the aperture portion of the first nozzle and the needle, and also from the second nozzle. Moreover, it is possible to vary the aperture area of the gap between the aperture portion of the first nozzle and the needle continuously, by shifting the needle along its axial direction by the needle position adjustment device. Accordingly, it is possible to adjust the first fluid supplied to the diffuser from a small flow to a large flow continuously. In particular, since it is possible to perform supply only from the second nozzle when a first fluid flow of small flow is being supplied to the diffuser, therefore at this time it is possible to reduce the wall resistance experienced by the first fluid flow.
The aperture portion of the second nozzle may be formed at the end portion of the needle, with the needle also serving as the second nozzle.
In this case, when a first fluid flow of small flow is supplied to the diffuser, it is possible to supply this first fluid flow to the diffuser from the second nozzle only, while, when a first fluid flow of large flow is supplied to the diffuser, it is possible to supply this first fluid flow to the diffuser from the second nozzle from the gap between the first nozzle and the aperture portion of the second nozzle, and also from the second nozzle (in the same manner, it would also be acceptable to supply the first fluid flow from the second nozzle to the diffuser). Moreover, when the first fluid flow is supplied to the diffuser from the gap between the first nozzle and the aperture portion of the second nozzle, it is possible to vary the aperture area of the gap between the first nozzle and the aperture portion of the second nozzle continuously by shifting the second nozzle along its axial direction by a second nozzle position adjustment device which serves as a needle position adjustment device. Accordingly, it is possible to adjust the first fluid supply to the diffuser continuously from a small flow to a large flow. In particular, since it is possible, when supplying a first fluid flow of small flow to the diffuser, to supply it from the second nozzle only, therefore at this time it is possible to reduce the wall resistance which the first fluid flow experiences, and it is possible to avoid deterioration of the stoichiometry when the flow is small. Furthermore, since there is no requirement to change over between nozzles, it is possible to apply this fluid supply device to a fuel cell for use in an automobile in which the required stoichiometry value changes continuously and moreover over a short time period.
It is also possible further to include a fluid supply interruption mechanism which, when the first fluid flow is to be supplied to the diffuser only from the second nozzle, interrupts the supply of the first fluid flow to the first nozzle.
It is also yet further possible for the fluid supply interruption mechanism to interrupt the supply of the first fluid flow to the first nozzle in accompaniment with the shifting of the second nozzle in its axial direction.
In this case, changeover of the supply conduit of the first fluid flow to the diffuser and variation of the area of the gap between the first nozzle and the aperture portion of the second nozzle may be simultaneously performed, just by simply shifting the second nozzle in its axial direction. Accordingly, it is possible to operate this fuel supply device with a single actuator.